In photolithography techniques, for example, there can be performed the steps of forming a resist film made of a resist composition on a substrate, selectively exposing the resist film to radiation such as light or electron beam through a photomask having a predetermined pattern formed thereon, and subjecting to a development treatment to form a resist pattern having a predetermined shape on the resist film. A resist composition in which the exposed area shifts to be soluble in a developing solution is referred to as a positive resist composition, whereas, a resist composition in which the exposed area shifts to be insoluble in a developing solution is referred to as a negative resist composition.
In recent years, advances in lithography techniques have lead to ongoing, rapid miniaturization of resist patterns in the production of semiconductor devices and liquid crystal display devices. As means for miniaturization, further progress has been made in shortening of the wavelength of exposure light. Although ultraviolet ray typified by g-ray or i-ray has conventionally been used, KrF excimer laser (248 nm) is introduced at present and ArF excimer laser (193 nm) begins to be introduced. A study has been made on F2 excimer laser (157 nm), EUV (Extreme Ultra Violet), electron beam and X-ray, each having a shorter wavelength.
To reproduce a pattern having a miniaturized size, a resist material having high resolution is required. As such a resist material, a chemically amplified resist composition containing a base resin and an acid generator which generates an acid under exposure is used. For example, a positive chemically amplified photoresist contains a resin component which exhibits increased alkali solubility under the action of an acid, and an acid generator component which generates an acid under exposure and, when the acid is generated from the acid generator under exposure during the formation of a resist pattern, the exposed area shifts to an alkali soluble state.
As the resin component of the chemically amplified positive resist composition, there can be commonly used a resin in which hydroxyl groups of a polyhydroxystyrene (PHS) based resin are protected with acid dissociable, dissolution inhibiting groups, and a resin in which carboxy groups of a resin (acrylic resin) comprising a structural unit derived from (meth)acrylic acid in the main chain are protected with acid dissociable, dissolution inhibiting groups.
As the acid dissociable, dissolution inhibiting groups, there can be used a so-called acetal group, for example, a chain ether group typified by a 1-ethoxyethyl group and a cyclic ether group typified by a tetrahydropyranyl group; a tertiary alkyl group typified by a tert-butyl group; and a tertiary alkoxycarbonyl group typified by a tert-butoxycarbonyl group (see, for example, Japanese Unexamined Patent Application, First Publication No. 2002-341538).
However, when a resist pattern is formed using such a material, there arises a problem that roughness (line edge roughness (LER)) occurs on the surface of a side wall of a pattern. A problem of LER becomes more serious as a trial of forming a higher resolution pattern is made. With further progress of miniaturization of a resist pattern, high resolution is further required and thus an improvement in LER becomes more important.